capture / AVI / render ... which steps do cost me quality losses?

[jmwismer]

Hi there,
I shot some DV, captured it, edited it, and made a DVD as I have done many. On that one though, I have a very annoying low frequency humming noise which is amplified by my home cinema setting. So I went on this forum, found lots of good info, and tried the following:
- made an AVI file from the original edited footage
- demuxed WAV audio from AVI file (VirtualDub)
- high pass filtered the WAV audio (Audacity)
- saved the AVI without sound to new AVI-no-sound (VirtualDub)
- remuxed AVI-no-sound with the filtered sound file (VirtualDub)
- re-rendered a DVD with this new AVI with filtered sound

It looks like I lost video quality in the process. Which steps are responsible for that? Is it because I render twice from my video editing program (Studio 8 ), once to AVI, then to DVD? Is saving to AVI files from VirtualDub altering quality?

I suppose that if I did the whole story directly from the AVI I get from my DVcam, I would not lose quality? (I had to do the filtering of a rendered AVI since I did all the editing work before realizing I had the humming noise problem).

thx for your help,
jm

[redwudz]

Do you mean you took the DVD file and used that to correct the audio? Or do you mean you used the DV file that had been edited?

The reason I'm asking is that if you are just working with the audio, you shouldn't have to re-encode any of the video.
If the video source is the DVD, you could use VOB2MPG and take out the MPEG-2 and the audio. No re-encoding. Then you process the audio and mux it back with the video, reauthor to a new DVD. But no video re-encoding.

Or if you are using the edited DV, just take out the audio as a WAV, process it, then add it back in. Disable or delete the old audio and select the new. Use Direct stream copy with both the audio and video and you should have a DV with replaced audio and no re-encoding of either. I use VirtualDub Mod for that as I like the way it handles audio better. Then you would have to encode it again to MPEG-2 and author it to DVD. You should have the same quality with the MPEG-2 file as you had before if you use the same settings.

Obviously it would be a lot less work to use the DVD files. Then you would just reauthor the DVD. I would also convert the WAV output from Audacity to AC3 with ffmpeggui before I author it again.

I use TMPGEnc DVD Author and it will accept elemental streams of audio and video. If your authoring program won't you may need to mux the audio back with the MPEG-2 video before authoring. You could do that with the trial version of TMPGEnc encoder or probably the trail version of TDA.

I hope that's not too confusing. The bottom line is that you shouldn't have to re-encode and lose quality.

[jmwismer]

thx Redwudz, not confusing at all, very helpful. Just me not a wiz. so just to make sure:

- I do not lose video quality when I mux / demux, directstream save AVI.

where do I lose quality?

- I guess when I render from AVI to MPEG for DVD
- do I lose quality when I render from my edited AVI on Studio 8 to AVI on my DV deck?

jm